Segment Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 02, 2015	Oct. 03, 2014	Jul. 04, 2014	Apr. 04, 2014	Jan. 03, 2014	Sep. 27, 2013	Jun. 28, 2013	Mar. 29, 2013	Jan. 02, 2015		Jan. 03, 2014		Dec. 28, 2012
Segment Reporting Information [Line Items]
Revenues	$ 73,611	$ 78,557	$ 76,574	$ 75,962	$ 72,772	$ 75,231	$ 75,505	$ 72,660	$ 304,704	[1]	$ 296,168	[1]	$ 292,653	[1]
Operating Income	14,133	19,238	16,084	14,094	12,342	15,160	17,593	10,851	63,549		55,946		57,620
Capital Expenditures									4,947		6,226		4,942
Depreciation and Amortization									5,404		4,951		4,711
Engineering and Other Scientific
Segment Reporting Information [Line Items]
Revenues									223,384		215,972		213,304
Operating Income									72,207		67,070		62,852
Capital Expenditures									3,719		5,180		3,264
Depreciation and Amortization									3,637		3,097		2,831
Environmental and Health
Segment Reporting Information [Line Items]
Revenues									81,320		80,196		79,349
Operating Income									25,145		25,072		25,752
Capital Expenditures									211		148		289
Depreciation and Amortization									197		299		286
Operating segments
Segment Reporting Information [Line Items]
Operating Income									97,352		92,142		88,604
Capital Expenditures									3,930		5,328		3,553
Depreciation and Amortization									3,834		3,396		3,117
Corporate
Segment Reporting Information [Line Items]
Operating Income									(33,803)		(36,196)		(30,984)
Capital Expenditures									1,017		898		1,389
Depreciation and Amortization									$ 1,570		$ 1,555		$ 1,594

[1] Geographic revenues are allocated based on the location of the client.